Shoulder preparation of teeth



w. c. ASHKIN 2,793,438 SHOULDER PREPARATION OF TEETH May 28, 1957 Filed July is, 1955 @QQBQ,

INVENTOR WILL/AM c ASH/(IN V B-Y 1 ATTORNEY United Sttes Patent srrouruun PREPARATION or TEETH William c. Ashkin, New York, N. Y.

Application July 13, 1955, Serial No. 521,762

2 Claims. (Cl. 32-58) This invention relates to new and useful improvements in the shoulder preparation of teeth. The invention more particularly relates to the grinding of the interproximal sides of a tooth in its shoulder preparation.

In dentistry, in order to fit teeth with crowns or porcelain jackets, it is first necessary to grind away a portion of the upper surface of the tooth and to leave a squarecut shoulder at about the gum line. The crown or jacket is then fitted over the reduced portion of the tooth so that the same rests on the shoulder and is secured in this position. The formation of this shoulder with the grinding away of a portion of the upper surface of the tooth is known in the dental art as the shoulder preparation of a tooth.

In the past, the shoulder preparation of the tooth was effected by means of a free-hand grinding, using small, abrasive grinding wheels and discs, such as diamond wheels and discs.

In order to effect this grinding, a good deal of manual dexterity and skill was required on the part of the dentist, and it was extremely difiicult to get an even and square shoulder, particularly at those portions about the circumference of the tooth which were difiicult to reach and see. This was particularly true in connection with the interproximal sides of the tooth, i. e., the mesial and distal sides, which, due to the close proximity of adjacent teeth, would require thin grinding discs, and had to be ground blind. This interproxirnal preparation required the highest dental skill and was an extremely intricate and time-consuming operation. Very often, in attempting to grind the shoulder, the dentist would grind too deeply, causing injury to the remaining tooth portion, or would form an irregular shoulder, which would not provide a satisfactory base for the crown or jacket.

In my co-pending application, Serial No. 521,761, filed July 13, 1955, the use of a novel clamp arrangement to provide a guide surface in the shoulder preparation of teeth is described. The guide surface of this clamp arrangement, however, can only extend along the lingual and buccal r labial side of the tooth, and therefore does not provide much aid in the preparation of the interproximal sides of the tooth.

One object of this invention is a method and a device which will allow an extremely uniform and accurate shoulder preparation of a tooth, particularly of the interproximal portions, and which requires a minimum of manual dexterity and skill. This, and still further objects will become apparent from the following description read in conjunction with the drawing, in which:

Fig. 1 is an exploded prospective view, showing complete equipment necessary for the interproximal shoulder preparation in accordance with the invention, and additionally showing interchangeable control wheels of various sizes in accordance with the invention;

Fig. 2 is a diagrammatic side elevation of a tooth, showing the proposed occluding surface preparation prior to the use of the device as shown in Fig. 1;

Fig. 3 is a side elevation showing the device in Fig. 1 in grinding position on a tooth;

Fig. 4 is a side elevation diagrammatically showing the device in Fig. 1 in grinding position with respect to an upper incisal tooth;

Fig. 5, is a diagrammatic side elevation showing the device of Fig. 1 in operating position with the position of the control wheel reversed; and

Fig. 6 is a vertical section of an embodiment of a tapered grinding disc in accordance with the invention.

In accordance with the invention, in order to effect the shoulder preparation, a guide surface is first formed on the occluding, i. e., the incisal or occlusal surface of the tooth. This guide surface may, for example, be formed by grinding, and should extend parallel to and above the shoulder to be formed. If the shoulder is to be a flat, i. e., a straight shoulder, the guide surface must be ground as a fiat guide surface. If a convex-shaped shoulder is desired, then the inclusal or incisal surface of the tooth should be ground with a corresponding convex-shaped guide surface. Thereafter, the shoulder is formed, using a grinding disc and a co-axially, adjacently positioned control wheel. The control wheel and the grinding disc should have respective sizes, so that the radius of the grinding disc exceeds the radius of the control wheel by an amount about equal to the axial distance of the tooth between the flat guide surface and the shoulder to be formed. The side portion of the tooth is ground away to form the shoulder, using the disc, while maintaining the control wheel in guiding contact with the flat guide surface. Since the axial depth of cut is accurately controlled by the control wheel, the shoulder may be formed at the interproxim-al surfaces of the tooth, practically automatically requiring a minimum of skill and practically no chance for error.

Generally, in the shoulder preparation of the tooth in order to prepare the same for a crown or porcelain jacket, the reduced portion of the tooth extending from the shoulder in a direction away from the gum line should be tapered. In accordance with a preferred embodiment of the invention, this tapering of the side wall portions of the tooth is effected with a dental grinding disc having an abrasive grinding surface inclined with respect to the plane ;of rotation of the disc by an amount corresponding to the degree of taper desired. An annular guide rim is also formed on the disc. This guide rim defines a guide surface which is free from abrasive and which is substantially parallel to the plane of rotation of the disc, i. e., normal to the axis of rotation of the disc. The guide rim surface extends as a continuation of the grinding surface, forming an angle of less than therewith. If the side portion of the tooth, which has been previously ground with the abrasive disc and the control wheel as described above to form the shoulder, is further ground with this tapered dental grinding disc, the same will grind away the side wall portion of the tooth until the abrasive-free guide rim contacts the side wall portion .of the tooth at the rootof the shoulder, preventing further grinding, and thus automatically forming the desired tapered shape of the tooth.

Referring to the drawings, 1 represents a conventional dentists mandrel or shaft having the flange portion 2 which is provided witha central female threadinto which the screw'd may be screwed. A conventional grinding disc, such as the diamond disc 3, may be held in this mandrel by placing the screw 4 through the central hole 3' of disc 3, and screwing it tightly into the thread in the flange 2 of the mandrel 1. The mandrel may then be placed in the conventional chuck or drill holder, and, upon rotation, the mandrel 1, along with the disc 3, will rotate.

In accordance with the invention, a bushing and a control wheel 6 are provided. "The control wheel 6 is in the form of a smooth metal disc of, for example, stainlesssteel, provided withvthe central bore 6'. The bushingS, which may, for example ,"be of brass or thelike, has an outer diameter somewhat smaller than the inner diameter of '6' and an axiallength somewhat greater than the width of the disc, so that the bushingS may 'thecentral hole 3' and through the bushing 5, and screwing the same into 1. Asthe mandrel l-rotates, the same will cause the bushing 5 to rotate and the disc 3to rotate with it, while the control wheel 6 may rotate freely on the bushing and thus be maintained stationary. A complete set of interchangeable control'wheels 6a, 6b, 6c, and 6d .may be provided, which'have different diameters, so that the device may be used for shoulder preparations in connection with teeth of various sizes.

. In use, in order, for example, to effect a shoulder preparation on the tooth 7, as indicated in Fig. 2, to'prepare the same for fitting with a crown or jacket, a flat guide surface is formed, as indicated by thedotted vlines 9, by grinding away the occlusal surface of the tooth With a conventional grinding wheel or disc. This guide surface should extend above and parallel to the shoulder to be formed, as, for example, the gum line 8.

After the guide surfaceis formed, a control wheel and disc of the proper respective sizes is chosen," so that the radius of the grinding disc exceeds'the radius of the control wheel by an amount substantially equal to the axial distance of the tooth between the flat guide surface and the shoulder tobe formed, i. e., by the distance A, as indicated in Fig. 3.

After the proper size control wheel and disc are chosen, the 'same are assembled on the mandrel 1 in the manner described above, and the same is fitted into the chuck or holder of the conventional dental drilling machine. The control wheel is then placed in contact .withthe fiat guide su1face'9, whichhas been formed on the tooth, and the side wall portion of the. tooth is ground away, leaving a reduced side wall portion as indicated by the/dotted lines markedilfl, leaving a shoulder at about the Since the axial depth of cut 'is limited by the control wheel 6, the shoulder will be accurately and gum line.

precisely formed, and it is only necessary 'for'the dentist to' maintain thecontrol Wheel 6 in contact withthe guide surface during the grinding.

"Prioror subsequent to the above-described grindinglof the interproximal surface of, the tooth, the lingual and 'buccal or labial side of the .tooth may be ground away, 'formingthe shoulder in the same rnanneror-in the coning may be effected in thesame manner as shown in Fig.

4. For convenience, it is possible, as shown in Fig. 5, to reverseqthe position of the control wheel 6 and the grinding .disc 3, provided 'thatthe control Wheel 6ris alder 10.

ways adjacent to the abrasive side of the disc 3, as should bethe lip of the bushing 5. As shown in Fig. 5, the other side of the tooth 7a is ground away to form the shoulder in this manner.

The grinding in the above-described manner will leave the ground-away side Walls of the tooth 10 substantially vertical and parallel to each other. In crown or jacket preparation, however, it is generally desirable to have these side walls tapering in a direction away from the gum in the manner shown by the dots marked 14 in Fig. 3. In order to automatically. effect this tapering of the tooth after the actual shoulder preparation, a tapered grinding wheel as shown in Fig. 6 may be used. This grinding Wheel has an abrasive grinding surface 12, which is inclined with respect to the plane of rotation of the disc by an amount corresponding to the degree of tapering 1d desired. A non-abrasive guide rim 11 is formed as a continuation of the abrasive cutting surface 12. This guide rim 11 extends parallel to the plane of rotation of thedisc, i. e., normal to the axis of rotation of the disc. The angle formed between the guide rim surfacell and the surface of the abrasive portion 13 will be an angle of less than In order to have the abrasive surface 12 and the non-abrasive surface 11 run smoothly into each'other as a continuation of each other,

it is necessary to form the under-cut 13, which is equal .in depth to the height of the abrasive layer, which is subsequently added, such as the abrasive diamond pieces. Withoutthis under-cut, after the abrasive would be added, the same would extend out past the surface 11, so that the surface 11 would not form a smooth continuation of the surface 12. In order to form on the tooth, it is merely necessary to mount this tapered grinding disc in a mandrel and hold the same so that its plane ofrotation is parallel to 10, and its edge 14 is adjacent to the shoul' The portion 10 is then ground away with the disc in this position, and when the guide rim 11 strikes theportion on the side wall it) adjacent to the shoulder the end of the shaft for rotation therewith anda control 'wheel of smaller diameter than said disc mounted on the shaft adjacent theabrasive side of the disc for free rotation with respect to the shaft and disc.

'2. Device according to claim 1, in which said control wheel is mounted for free rotation on a bushing positioned on said shaft adjacent said abrasive tooth-grinding disc for rotation therewith.

References Cited in the file of this patent UNITED STATES PATENTS 2,685,738 Leif Aug. .10, 1954 2,735,181 Carpenter Feb. 21, 1956 FOREIGN PATENTS 894,664 Germany Oct. 26, 1953 

